actually, at the start before the anime started airing, hijikata was originally going to be the main charakter, with his appearance identical to the one of gintoki. and have heard it was because the makers somehow lost the original design that was going to be gintoki's they took hijikatas original design and made a new one for hijikata gintama.wikia.com/wiki/Hijikata_Toushirougintama.wikia.com/wiki/Sakata_Gintoki